Occupation and Release Behavior of Guest Molecules in CH₄, CO₂, N₂, and Acetone Mixture Hydrates: An In Situ Study by Raman Spectroscopy

다국어 초록 (Multilingual Abstract)

<P>For practical applications of gas hydration (formation of gas hydrates) in environmental and technological processes, considerable knowledge regarding the thermodynamic stability and structural features of these hydrates, as well as the occupation behavior of specific components of gas mixtures within them, is essential. Herein, the hydrate phase equilibria of a system comprising CH<SUB>4</SUB>/CO<SUB>2</SUB>/N<SUB>2</SUB> (55/40/5) + aqueous acetone solutions (1, 3, and 5.56 mol %) were determined in the temperature range 273–285 K and under pressures up to 4.5 MPa. Gas compositions in the hydrate phase were also obtained by evaluating the following variables: (1) hydrate-formation temperature and pressure, (2) concentration of acetone, and (3) type of hydrate structure: (a) structure I or (b) structure II. The crystal structures of the gas hydrates formed from the acetone and CH<SUB>4</SUB> + CO<SUB>2</SUB> + N<SUB>2</SUB> mixture gas were also evaluated by both X-ray diffraction and Raman spectroscopy. In addition, structural identification of the CH<SUB>4</SUB> + CO<SUB>2</SUB> + N<SUB>2</SUB> + acetone hydrates formed by varying the concentration of acetone (0, 1, 3, and 5.56 mol %) was performed. Further evaluation of the temperature-dependent occupation behavior of CH<SUB>4</SUB> and CO<SUB>2</SUB> in structure II hydrate cages in the temperature range 150–290 K indicates that CH<SUB>4</SUB> and CO<SUB>2</SUB> gradually escaped from the hydrate frameworks with increasing temperature, up to 255 K, at which point the CH<SUB>4</SUB> + CO<SUB>2</SUB> + N<SUB>2</SUB> + acetone hydrate completely decomposed.</P>